30 PATHOGENIC BACTERIA. 



these conditions the bacteria appear as solidly-colored 

 spheres, rods, or spirals, as the case may be. 



By careful staining of appropriate organisms a sug- 

 gestion of internal structure beyond what has been men- 

 tioned can be shown. Thus, in some of the bacilli dis- 

 tinct "polar granules," rounded or oval, unstained 

 bodies are observed at the ends of the cell. What their 

 significance may be is unknown. A few bacilli may be 

 observed which contain within them a row of deeply- 

 stained granules, giving the organisms somewhat the 

 appearance of a streptococcus chain. These are called 

 metachromatic granules and are of unknown significance. 

 The Bacillus megatherium is peculiar in having its pro- 

 toplasm filled with small granules which stain more 

 deeply than the bacilli themselves. The diphtheria 

 bacillus and the cholera spirillum stain very irregularly 

 in fresh cultures, as if the tingeable substance was not 

 uniformly distributed throughout the protoplasm. Vacuo- 

 lated bacteria and bacteria that will not stain or stain 

 very irregularly may usually be regarded as degenerated 

 organisms, which, because of piasmolysis or solution, can 

 no longer stain homogeneously. 



The cell-walls of some of the bacteria seem at times to 

 undergo a peculiar gelatinous change or to allow the ex- 

 udation of gelatinous material from the protoplasm, so 

 that the individuals appear surrounded by a distinct halo 

 or capsule. Such capsules are seen to excellent advan- 

 tage by the pneumococcus as found in blood or sputum, 

 Friedlander's bacillus as seen in sputum, and by the Bacil- 

 lus aerogenes capsulatus in blood or tissue. This is not 

 only a peculiarity of certain individuals, but one which 

 only takes place when they develop under certain condi- 

 tions; thus, Friedlander points out that the capsule of 

 his pneumonia bacillus, when it was found in the lung or 

 in the "prune-juice" sputum, was very distinct, while 

 it could not be demonstrated at all when the organisms 

 grew in gelatin. 



From the cell-walls of many bacteria numerous deli- 



